There are various apparatuses and methods for the noncontacting measurement and control of objects, for example of objects in the form of threads, wire, rods or tubes, wherein, as a rule, a modulated beam of light, generally a laser beam, is guided over the object and focussed on a photodetector, the shading time recorded by the photodetector being, under certain conditions, a measure of the dimension of the object to be measured. Bringing about as linear a function as possible between the dimension to be measured and the shading time can be achieved in various ways, including the use of a suitable objective. In this case, with increasing measuring speed and increasing size of the object to be measured, ever greater demands are made on the measuring system and on the optical system. An objective which can be used for such measuring purposes is a telecentric F-theta-corrected objective. This means that the emergent central ray of the laser beam lies parallel to the optical axis for all angles of deflection during the scanning and that there is a linear relationship between this angle of deflection for the entering beam and the linear height of the image space. Known telecentric systems have the disadvantage, however, that the costs of the objective rise very steeply on enlargement of the field of measurement and it is therefore the object of the present invention to provide a measuring apparatus having a telecentric, F-theta-corrected objective which can be produced economically and permits rapid and accurate measuring and monitoring.